Such an air separator which--insofar as it is also used for gases other than air--is more generally also called a degassing device, is known for example from the laid open British patent application 2 063 108. The air separator described there has an essentially circular cylinder-shaped, perpendicularly arranged chamber to whose upper end an inlet is so arranged that the liquid to be degassed enters essentially tangentially in the area of the outer periphery. Because of the tangential introduction, the liquid to be degassed flows firstly on a circular flow path which is however overlaid by the total flow through the perpendicular chamber, with the result that the liquid flows through the chamber on a helical flow path. A tangentially arranged outlet is appropriately provided at the lower end, so that the degassed liquid can emerge. The degassing effect is effected in the case of the generic air separator or the degassing device through the creation, by the circular movement elements of the liquid flow, of centrifugal forces which build up pressure differences in the liquid, with the result that the less dense, i.e. lighter air bubbles are driven to the centre of the chamber and rise along the longitudinal axis of the chamber until they are removed through a ventilation bore.
The described air separator is used in particular for the degassing of blood. It is necessary to separate blood from possibly contained gases whenever blood is removed from the natural blood circulation of a patient and is guided by an artificial blood circulation before it is guided back again into the body of the patient. This occurs for example during cell separation within the framework of the autotransfusion of blood during operations, also during haemodialysis or haemofiltration, and in mixed forms of these treatment techniques.
In particular during the degassing of blood, the problem arises that, although on the one hand the separation of contained air bubbles must take place with great reliability, as air bubbles possibly remaining in the blood can lead to the death of the patient, on the other hand the air separator must however be so composed as regards its mechanical properties and the developed flow form that damage to the blood constituents is avoided. A good wash-out behaviour of the air separator is desirable for a low level of blood damage, which goes along with smooth surfaces on the material side and with a flow-favourable continuous structure of the flow paths, with the result that the adhesion of blood corpuscles to surfaces of the air separator and thus a conglomeration of blood corpuscles is avoided. Short residence times of the blood in the air separator are also conducive to a low level of blood damage, but without making the air separation as such worse, plus a small fill volume.
For air separators used in hospitals, it is also desirable that they can be easily secured and can be fitted without great outlay into already existing tube lines. For this reason it is desirable that inlet and outlet are arranged aligning coaxially with each other, so that the air separator can, for example after the cutting open of an existing tube, be fitted into the latter without having to change the tube guidance. Furthermore, the tube guidance at dialysis machines can for example can take place without unnecessary loops and the production process for a prefabricated unit consisting of air separator and tube is simplified, as the tubes can be assembled automatically.
In all systems affecting the safety of a patient, a constant checking facility is also desirable, so that an optical monitoring of the fill level is to be possible. Capacitive fill-level monitoring systems are also conceivable, for whose proper functioning a good wash-out behaviour is again necessary, in order to prevent residual blood from remaining in the air separator.
The air separator known from the cited British patent application only partially meets the requirements cited above. In particular, it has no coaxial connections or sockets lying in the longitudinal direction of the chamber, with the result that it is awkward to handle and the wash-out behaviour does not meet a high level of requirements.
Since, on the other hand, the helical flow development guarantees a good air separation, the object of the invention is first to provide an air separator which retains the advantages of the helical flow guidance and nevertheless makes possible connections or sockets, arranged coaxial relative to one another, lying in the longitudinal axis of the air separator.
In particular when using a generic air separator for the treatment of blood, it is desirable in the hospital sector if the air separator itself is designed as a disposable part, i.e. if it can be replaced and disposed of after a certain period of use and in particular naturally after a change of patient, as a cleaning which would satisfy the hygiene requirements of the hospital would not be justifiable in terms of outlay. A further object of the present invention is therefore to realize the advantages described above which are to be achieved by means of a newly to be created air separator, in such a way that the proposed air separator is producible at favourable cost in large numbers from customary plastics, in particular by injection moulding.